1. Field of the Invention
The invention relates to a tree shear blade or cross-cut blade as used in a mechanical tree felling device.
2. Prior Art
Tree felling devices using shear or cross-cut blades are old and can be divided into two main types. One type is a "feller buncher" in which two similar blades are mounted on a scissor-like mechanism used primarily by a carrier with a hydraulically operated boom. The two blades close simultaneously by hinging about a pivot point and sever the tree which is held by clamps or grapples. The second type is a single blade cutter which is commonly mounted on a crawler- or loader-type carrier. The single blade is generally thicker than the scissor type blade and is commonly designed to cause a tree to fall in a particular direction for later gathering.
Both types of shear blades as above identified commonly cause splitting or crushing damage to severed trees far in excess of what would be anticipated by normal falling when using an ax or chain saw. The splitting tends to run longitudinally from the cut and up the butt of the tree, sometimes extending six to ten feet up the butt, depending on the species and condition of the tree. This splitting tendency of the tree is well known and many attempts have been made to reduce the splitting. To reduce the amount of wood that is compressed when the blade severs the tree, blades have been made thinner but such blades are mechanically weak. Sometimes the thin blades are strengthened by ribs on a surface of the blade but, to the inventor's knowledge, these ribbed thin blades have not reduced the splitting tendency appreciably. One such attempt to strengthen thin blades is disclosed in Canadian Pat. No. 980,664, inventor Thomas A. McLaughlan, and, whilst this blade has a tendency to reduce splitting when compared with earlier shear blades, according to some authorities, this blade still causes more damage to trees than would be expected with chain saw or ax felling techniques.